This kind of AC-AC direct conversion device previously existing is a conversion device which quickly switches a bidirectional switch having self arc-extinguishing type semiconductor elements and converts a single-phase or multi-phase AC input to power of arbitrary voltage or frequency, and it is configured as shown in FIG. 1.
FIG. 1 shows a basic configuration of a three-phase/three-phase AC-AC direct conversion device. A three-phase AC power source 1 is connected to an arbitrary load 4 through an input filtering part 2 formed by a reactor and a capacitor and a semiconductor power conversion part 3 formed by nine bidirectional switches SW1˜SW9. Regarding the nine bidirectional switches SW1˜SW9, although its detailed configuration manner, such as a case where the bidirectional switches SW1˜SW9 are configured by 18 reverse-blocking IGBTs and a case where the bidirectional switches SW1˜SW9 are configured by combination between a semiconductor element of a normal IGBT etc. and a diode, is not limited, the bidirectional switches SW1˜SW9 are configured by switching elements that can bidirectionally exchange power.
Here, as shown in FIG. 1, in the following, power source three phases are expressed as RST phases, and output three phases are expressed as UVW phases.
The AC-AC direct conversion device, typified by the matrix converter, is a device that directly converts power from AC to AC as a configuration of combination between a voltage-fed power converter that generates an output voltage by PWM-controlling a power source voltage and a current-fed power converter that generates a power source current by the PWM-control with an output load current regarded as source of current. To simultaneously achieve both controls by the nine bidirectional switches, both are linked with each other in the control (namely that the controls have constraints that three-phase instantaneous effective power exchanged by input and output is required to be coincident with each other).
Next, on the basis of the foregoing, a space vector of the AC-AC direct conversion device will be defined. Since the output voltage is generated from the AC power source voltage by the PWM and an input current is also generated from the AC load current by the PWM, unlike a space vector of a normal DC-AC conversion device (inverter), a PWM-controlled instantaneous space vector which the AC-AC direct conversion device can produce momentarily varies. The variation of the instantaneous space vector of the output side voltage depends on phase•magnitude of the power source voltage that is a source chopped up by PWM. The instantaneous space vector of the input side current varies depending on phase•magnitude of the output load current.
With respect to a switching pattern of the AC-AC direct conversion device, there is a need to provide constraints that (1) the power source must never be shorted, (2) the load current must not be a discontinuous current. (1) is for preventing an overcurrent breakage caused by the power source short circuit, and (2) is for preventing an overvoltage failure caused by energy stored in an inductance of inductive load. When taking these conditions into consideration, the switching patterns of the nine bidirectional switches SW1˜SW9 are limited to 27 (33) varieties of combinations.
When expanding the 27 (33) varieties of switching patterns for the input side and output side onto a static αβ coordinates, they can be represented as shown in FIGS. 2A, 2B and Table 1 (FIG. 2A shows space vectors of the input side current at output load current phase 15 degrees, FIG. 2B shows space vectors of the output side voltage at power source voltage phase 15 degrees).
TABLE 1MCMCI/OswitchconnectON stateGroupStateUVWUVWS1simple1s1-1aRSS158harmonic2s1-1bSRR247oscillation3s1-2aSTT2694s1-2bTSS3585s1-3aTRR3476s1-3bRTT169S2simple7s2-1aSRS248harmonic8s2-1bRSR157oscillation9s2-2aTST35910s2-2bSTS26811s2-3aRTR16712s2-3bTRT349S3simple13s3-1aSSR257harmonic14s3-1bRRS148oscillation15s3-2aTTS36816s3-2bSST25917s3-3aRRT14918s3-3bTTR367R1counter-19r1-1RST159clockwise20r1-2TRS348rotation21r1-3STR267R2clockwise22r2-1RTS168rotation23r2-2SRT24924r2-3TSR357Znull25z1RRR14726z2SSS25827z3TTT369
In Table 1, the space vectors are separated into the following six groups; a simple harmonic oscillation vector S1 which is a group of simple harmonic oscillation vector with a direction of phase angle 30 degrees being a positive axis, a simple harmonic oscillation vector S2 with a direction of phase angle 150 degrees being a positive axis, a simple harmonic oscillation vector S3 with a direction of phase angle 270 degrees being a positive axis, a rotation vector R1 whose length is a maximum and constant and which rotates counterclockwise, a rotation vector R2 whose length is constant and which rotates clockwise, and a zero vector Z which is fixed at a center zero point of hexagon. Each of these base vectors depends on phase θ of an input voltage, i.e. each of these base vectors varies in synchronization with angular velocity ωi of the input voltage. Further, a length of the vector (size of the hexagon) corresponds to a magnitude of an input line voltage.
As described above, because the instantaneous space vector momentarily changes, the vector varies with the each phase. When focusing attention on a direction of the variation of the instantaneous space vector in the static αβ coordinates, 27 varieties of vectors can be classified into 18 varieties of simple harmonic oscillation vectors (6 varieties of vectors for each of three axes, phase relationship is constant) and 6 varieties of rotation vectors (3 varieties of vectors in the clockwise direction and 3 varieties of vectors in the counterclockwise direction, each length of them is constant) and 3 varieties of zero vectors (it is unchangeable at an origin point).
Table 1 is an example in which the 27 varieties of patterns are classified with the output side space vector being a reference. Such basic idea of the space vector is already known by a Non-Patent Document 1 etc.
Next, an idea of the space vector will be simply explained. For instance, in the output side space vector, when focusing attention on a state 1: a connection pattern of UVW=RSS in Table 1, a three-phase AC of the output has phase differences of each 120 degrees in order of U phase→V phase→W phase. Since the output side space vector is defined with U phase being α axis (S1 axis in FIG. 2) here, V phase is an S2 axis direction, W phase is an S3 axis direction.
In the state 1: UVW=RSS, same as the example of FIG. 2, when the power source voltage phase θ is 15 degrees, a relationship of the power source phase voltage becomes a relationship of vr>0>vs>vt. Thus, in the state 1, Vu*=Vr, Vv*=Vs, Vw*=Vs. Since Vr is a positive voltage and Vs is a negative voltage, when synthesizing Vu*, Vv* and Vw*, as shown by vRSS in FIG. 2, the output side space vector is outputted in S1 axis positive direction. Also regarding the other instantaneous space vectors, they can be expanded likewise.
Now, as shown in FIG. 3, a domain of the input side space vector is divided for each 30 degree phase as shown in FIG. 3A, and a domain of the output side space vector is divided for each 60 degree phase as shown in FIG. 3B, and numbers are given. In the following, these are called sectors. The sector can be discriminated when determining input phase θ and output phase φ from the following three-phase two-phase conversion (αβ conversion) and trigonometric function.
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                                                 1                          2                                                                                                                                    -                                                  1                          2                                                                                                                                                0                                                                                                                3                                                2                                                                                                            -                                                                              3                                                    2                                                                                                                    ]                            ·                              [                                                                                                    Vu                        *                                                                                                                                                Vv                        *                                                                                                                                                Vw                        *                                                                                            ]                                                    ⁢                                                      (        1        )                                [                  Expression          ⁢                                          ⁢          2                ]                                                                                  θ            in                    =                                                    tan                                  -                  1                                            ⁡                              (                                                      Ii                    ⁢                                                                                  ⁢                                          β                      *                                                                            Ii                    ⁢                                                                                  ⁢                                          α                      *                                                                      )                                      ⁢                                                  ⁢            when            ⁢                                                  ⁢            power            ⁢                                                  ⁢            factor            ⁢                                                  ⁢            is            ⁢                                                  ⁢            1                          ⁢                                  ⁢                                            θ              in                        =                                          tan                                  -                  1                                            ⁢                              (                                                      Vi                    ⁢                                                                                  ⁢                    β                                                        Vi                    ⁢                                                                                  ⁢                    α                                                  )                                              ,                                          ⁢                                    θ              out                        =                                          tan                                  -                  1                                            ⁡                              (                                                      Vo                    ⁢                                                                                  ⁢                                          β                      *                                                                            Vo                    ⁢                                                                                  ⁢                                          α                      *                                                                      )                                                                        (        2        )            
Here, as a present invention-related art, a space vector modulation method of the matrix converter described in a Non-Patent Document 2, and a PWM control method of the matrix converter described in a Non-Patent Document 3, etc. are known.
In previously existing typical control systems (for example, the Non-Patent Document 2), there are many systems in which input and output waveforms can be converted to sine waves without using output load current information. Since information required for the PWM-control of the matrix converter is only information of phase (or phase and magnitude) of three-phase AC power source voltage and also information of an output current detection value is not included in an operation, the control can meet an open-loop control.
On the other hand, when focusing attention on the number of times of switching within one control cycle, in the case of the previously existing typical control systems, it is four times or more (when counting within carrier one cycle, it is eight times or more).
Here, the one control cycle is a PWM cycle. If the system is five-vector modulation system, the cycle is a total time of pulse signals (output times) of five space vectors. It is a unit time required for PWM of the five instantaneous space vectors, i.e. a unit time required to fit the five instantaneous space vectors to a command value through integration (on average), and normally, update of the command value is also synchronized with this unit time.
However, when applying it to such a triangular wave carrier comparison system as described in the Non-Patent Document 3, because it corresponds to a case where the command value is updated at a peak and a valley of the triangular wave, a generally-called carrier frequency becomes ½ times of a control frequency.
For example, carrier 5 kHz→control frequency 10 kHz (one control cycle=100 μs). If the system is five-vector system, one control cycle is organized by five PWM pulses, namely, that the number of times of switching is four times. Further, in a case of four-vector modulation system, one control cycle is organized by four PWM pulses, and the number of times of switching is three times.
Non-Patent Document 1: Akio Ishiguro, Takeshi Furuhashi, Muneaki Ishida, Shigeru Okuma, Yoshiki Uchikawa: “Output Voltage control Method of PWM-Controlled Cycloconverters with Space Vectors”, The Transactions of the Institute of Electrical Engineers of Japan, Vol. 110, No. 6, pp, 655-663 (1990)
Non-Patent Document 2: Yugo Tadano, Shota Urushibata, Masakatsu Nomura, Tadashi Ashikaga: “A Study of Space Vector Modulation Method for Three-Phase to Three-Phase Matrix Converter”, Heisei 18 Annual Conference of the Institute of Electrical Engineers of Japan, Industry Society, 1-87 (2006)
Non-Patent Document 3: Yusuke Andou, Takaharu Takeshita: “PWM Control of Three-Phase to Three-Phase Matrix Converter for Reducing Number of Commutations”, Heisei 18 Annual Conference of the Institute of Electrical Engineers of Japan, Industry Society, 1-04-4 (2006)